what is the order of zues siblings oldest to youngest?

The real order of the 1st Generation by birth (pre-eaten) is: Hestia, Hades, Demeter, Poseidon, Hera, & then Zeus/Post-Eaten: Zeus, Hera, Poseidon, Demeter, Hades, & then Hestia.

Hestia is considered as the 1st & the last because she was born 1st, but regurgitated last, so through this way she would be the eldest & youngest child. Zeus was the last child to be born, but was never swallowed. He was hidden until grown, where he then forced his Father to release his siblings. They returned in reverse order they were born.